Fuel cells use hydrogen and oxygen to produce electricity, and many fuel cells that produce electricity are more efficient than internal combustion engines. Air is typically used for the oxygen supply, but hydrogen is not readily available at many locations. Hydrogen can be produced from liquid hydrocarbon fuels in a hydrogen production system, which is sometimes referred to as a fuel reformer, and liquid fuels have several advantages over hydrogen. For example, liquid fuels do not require high pressure storage tanks like hydrogen gas, liquid fuels typically have a higher energy density than hydrogen, liquid fuels are denser than most compressed gases so less storage space is needed, and liquid fuels are more readily available as mentioned above.
The fuel reforming reaction combines a liquid hydrocarbon fuel with oxygen to produce hydrogen gas, carbon monoxide, and may produce some carbon dioxide in a reformate stream, where the oxygen may be provided in air, steam or other sources. The steam reforming reaction (sometimes referred to herein as the “reforming reaction”) is endothermic, but the fuel used for the reforming reaction can also be combusted in a combustion reactor to provide the heat needed to drive the reforming reaction. The reformate stream may be combined with more superheated steam and then subjected to a water gas shift reaction to produce carbon dioxide and hydrogen from carbon monoxide and water. In some embodiments the fuel reforming reaction takes place at about 700 to about 1,100 degrees centigrade (° C.) and about 3 to about 25 atmospheres pressure, and the water gas shift reaction takes place at about 200 to about 450° C. and about 1 to about 20 atmospheres pressure. After the water gas shift reaction, the hydrogen may be cooled down to remove water by condensation before use in a fuel cell. The widely varying temperatures and pressures briefly summarized above can be maintained with heat exchangers and pressure control mechanisms.
In some embodiments, the size and weight of the hydrogen production system and fuel cell are limited. For example, size and weight are important parameters for components in aircraft. The high pressures involved in some of the reactions typically require a vessel with walls that are thick enough to withstand the temperatures and pressures involved. However, thicker walls increase the size and weight of a reformer and limit aerospace applications.
Accordingly, it is desirable to provide a hydrogen production system with reduced weight compared to typical hydrogen production systems with thick, heavy, high pressure containment walls. In addition, it is desirable to produce a hydrogen production system where the various components are combined so they occupy less space than a plurality of vessels. Further in addition, it is desirable to provide a hydrogen production system with transition and interconnect ducting, and with high thermal integration that may improve efficiency. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.